Congestive heart failure is a condition in which the heart is unable to pump enough blood to the body's other organs. The New York Heart Association (NYHA) Functional Classification provides a way to classify heart failure patients based on how much the patient is limited during physical activity. For example, Class 1 patients suffer no symptoms from ordinary activities; Class 2 patients experience a slight, mild limitation of activity and are comfortable with rest or with mild exertion; Class 3 patients experience a marled limitation of activity and are comfortable only at rest; and Class 4 patients should be at complete rest, confined to bed or chair, and symptoms occur even at rest.
Congestive heart failure patients are initially treated during NYHA Classes 1-3 stages of this degenerative disease. For patients that do not respond to these treatments and degrade to Class 4, ventricular assist devices (VADs) are often utilized as a last resort either as a bridge to heart transplant surgery or, in most critically ill patients who are ineligible for transplant, as a destination therapy. The VADs typically consist of displacement, centrifugal, or axial-flow blood pumps. These devices are often thought of as a last resort because the pumps currently have a limited life, typically on the order of 2-3 years. Following that time period, the device must be replaced. Although many companies are developing longer life products, these do not yet currently exist.
A secondary complication for these VADs is that blood must be routed from the patient's heart to the pump and then returned to the arterial supply via an aortic cannula. Since this requires blood flow through one or more man-made devices, a significant concern is clotting, pannus formation within the cannula, and complications from medications used to counter thrombus formation. Currently, no pump exists that allows a patient freedom from anticoagulation medications and the side effects thereof. Additionally, since blood must pass through the pump, the blood is often passing over bearings or within channels that both present thrombus and hemolytic concerns.
Yet another complication with VADs is that a proper balance between flow rates and patient activity must be maintained. Specifically, in order to provide the patient benefit, the pump must provide the necessary flow rate while still allowing the aortic valve to open and close to prevent thrombus formation and stroke potential. The pump must accomplish all this within the various ranges of patient activities. Typically, with current VADs, a patient provides this control by selecting from a series of pump settings.
In summary, VADs are a last resort because use of VADs involves numerous complications due to associated medications, thrombotic and hemolytic concerns, and the effective life of the current VADs. As such, VADs do not provide effective therapies for those heart failure patients between NYHA Class 1 and end-stage Class 4.